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How can you prevent a PLC failure?

Published: 05/08/2022

How can you prevent a PLC failure?

Designed in the late 1960s by Dick Morley, programmable logic controllers (PLCs) took the industrial market by storm. Capable of making data based decisions and providing exceptional levels of control for a variety of applications, it is clear to see why. Despite their ruggedness, they are not immune to breaking down. When a fault occurs within your PLC, identifying the root cause can be a substantial challenge. However, there are a number of key indicators which can assist you in isolating the fault and even prevent it from arising, avoiding costly unplanned downtime.

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What are the most common causes of PLC failure?

I/O Modules and Field Devices

The main cause of PLC failures are down to I/O modules, field devices or power supply issues. In fact, 80% of PLC failures are caused by one of these faults, predominantly indicated by either stopping suddenly or being irregular in its performance. When this happens, the engineer diagnoses where the sequence has stopped by interrogating the software ‘on-line’, so that they can trace the problem to a specific I/O module and input or output point.
Tracing the fault to a specific point helps the engineer find the all important root cause. This could be due to a PLC configuration failure, loose terminal block, tripped circuit breaker, issues with wiring or even a failure of a 24V DC supply.

Power Supply Issues

A predominant reason PLCs can fail is due to loose or corroded connections. A lot of companies commonly have redundant power systems or they will install uninterruptible power supplies (UPS) in order to keep things running in case of a mains power failure. This provides greater control of assets to maintain its safe operation.
When power is lost, it is possible that the PLC could lose its memory, affecting all operational programs. To avoid this, a PLC sometimes has a backup battery which ensures the device restarts correctly. It is important that you backup all PLC Software frequently and store it safely and securely. If software is not backed up on a regular basis and something does go wrong, downtime will be prolonged significantly while the program is re-written.

Interference

Industrial environments that contain a variety of electrical equipment commonly experience electromagnetic interference (EMI) and radio frequency interference (RFI). Anything from small radio transmitters to huge motors can cause this interference. It is very important for industrial environments to control electrical noise as it can cause unusual behaviour, intermittent faults and ultimately, a PLC failure.

How can you minimise electrical noise and interference?

  • Relocate Sensitive Equipment
  • Grounding
  • Shielding Cables Between Sensitive Equipment
  • Segregate Systems with High Power Components and Add Barriers

Network and Communications

It is vital that most PLCs communicate with devices such as HMIs and other equipment, however sometimes communication can be lost between said devices. You can reduce the likelihood of communication failures by making sure that the physical network infrastructure is installed and terminated correctly. It is also important that when adding more devices, they are suitable for the purpose and the firmware patches are installed frequently to maintain reliable and secure operation.

Heat

Is the operational environment suitable for the equipment and control systems? Without air filtration components in the cabinets, there is insufficient airflow which causes components to overheat, resulting in the dreaded downtime. If equipment goes over the manufacturer's recommended temperature, it is likely to fail. High humidity also causes condensation on electrical products, once again leading to a PLC failure. To prevent this, make sure you think carefully about where a control panel is located when installing it and/or use panel-cooling systems, a popular solution in many industrial plants.

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Preventative Maintenance and Your PLC - Minimising Risk

1. First up, keep an eye on climbing temperatures and the overall environmental factors which could potentially impact your device. Humidity, temperature and other factors play an important role in the longevity and efficient running of your components. Taking a look at the manufacturer guidelines will give you an appropriate temperature range which is deemed safe for your PLC.

2. Make sure your unit is free from debris and dust. Ensuring sufficient ventilation protects your circuit board from dust which could otherwise easily result in it short circuiting.

Clean or replace all filters installed in enclosures. This allows your PLC to get the maximum airflow and ensures consistency of output.

3. Loose connections can of course cause short term damage but goes beyond and can even result in lasting damage to the components within your PLC. You must ensure all connections are tightly fitted with particular focus on your I/O modules. Also inspect this module and determine whether any adjustments need to be made. Wiring integrity is key!

4. Backup your PLC program. Very little more needs to be said here. Without a backup, you will fall victim to prolonged periods of downtime. This is especially disastrous if your original equipment manufacturer (OEM) has deemed the device obsolete, making locating a program increasingly difficult.

5. Finally, Batteries and UPS systems should be tested frequently. The LED indicator will tell you if it needs replacing. This will ensure that systems are reliable and operate continuously even if a power fault did occur.

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How can Northern Industrial help you and your PLC?

No fix no fee may sound too good to be true but here at Northern Industrial, we make it a reality. Our repair service is here to ensure your programmable logic controller is optimised, fully functioning and reliable as a Nokia 3310, no matter the brand.

Here at our 20,000 sq ft repair facility, highly trained engineers utilise bespoke test rigs, providing the most efficient and cost effective solution for all types of PLC modules:

> CPU modules
> Power supply modules
> I/O modules
> Interface modules
> Communication modules
> Memory modules
> Special function modules
> Expansion modules
> Programming devices

Our electro-mechanical and cosmetic rebuilds are undertaken right down to component level and with our award winning PLC repair test facility accredited to British and International standards (including ISO 9001 certification), you are guaranteed a top shelf service. Our team is here to provide you with the support you need if your PLC manufacturer deems a range obsolete. If you are currently using a legacy system, we are ready and waiting to maintain it so the wheels of your production do not grind to a halt.

The Northern Industrial technicians know the perils of having to reprogram a PLC. That is why we offer a program and parameters backup service in addition to your repair. No waiting around while the program is rewritten and no costly downtime. The PLC is simply returned to you, reinstalled and it is ready to rock and roll.

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Are you in control of your PLC repairs?

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